Technique to reduce the zeolite molecular sieve solubility in an aqueous system

ABSTRACT

An improved process for separating a component from a feed mixture comprising an aqueous solution of a mixture of different components, such as a mixture of saccharides. In the process the mixture is contacted with a zeolite which selectively adsorbs a component from the feed mixture. The adsorbed component is then recovered by contacting the adsorbent with a desorbent material such as water to effect the desorption of the adsorbed component from the adsorbent. There is an undesirable tendency for the silicon constituent of the zeolite to dissolve in the aqueous system. The improvement to the process comprises the impregnation of the zeolite with a binder material comprising a water permeable organic polymer which substantially reduces the undesirable dissolution. The adsorbent is manufactured by mixing together powder of the zeolite, powders of the organic polymer binder, and a liquid organic solvent, extruding the mixture into an extrudate and drying the extrudate.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of my prior co-pendingapplication Ser. No. 171,864 filed July 24, 1980 and now abandoned,which is a division of my prior application Ser. No. 48,955 filed June15, 1979 and issued on Feb. 3, 1981 as U.S. Pat. No. 4,248,737, thecontents of both applications being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of art to which this invention pertains is solid-bedadsorptive separation. More specifically, the invention relates to animproved adsorbent, method of manufacture of the adsorbent and improvedprocess for separating a component from a mixture comprising an aqueoussolution of a mixture of different components which process employs anadsorbent comprising a crystalline aluminosilicate which selectivelyadsorbs a component from the feed mixture.

2. PRIOR ART

It is known in the separation art that certain crystallinealuminosilicates referred to as zeolites can be used in the separationof a component from an aqueous solution of a mixture of differentcomponents. For example, adsorbents comprising crystallinealuminosilicates are used in the method described in U.S. Pat. No.4,014,711 to separate fructose from a mixture of sugars in aqueoussolution including fructose and glucose.

It is also known that crystalline aluminosilicates or zeolites are usedin adsorption processing in the form of aggolomerates having highphysical strength and attrition resistance. Methods for forming thecrystalline powders into such aggolomerates include the addition of aninorganic binder, generally a clay comprising silicon dioxide andaluminum oxide to the high purity zeolite powder in wet mixture. Theblended clay zeolite mixture is extruded into cylindrical type pelletsor formed into beads which are subsequently calcined in order to convertthe clay to an amorphous binder of considerable mechanical strength. Asbinders, clays of the kaolin type are generally used.

Zeolite crystal and inorganic binder agglomerates have long been knownto have the property of gradually disintegrating as a result ofcontinuous contact with water. This disintegration has been observed asa silicon presence or contamination in the solution in contact with theadsorbent. Such contamination may at times be sufficiently severe toimpart a cloudy appearance to the solution.

U.S. Pat. No. 3,262,890 discloses the use of cellulose acetate bondedzeolite particles as a desiccant for a refrigerant, such as ahalogenated fluorocarbon, in a refrigeration system.

U.S. Pat. No. 3,951,859 discloses molecular sieving particles comprisingadsorbent powders dispersed in a matrix of microporous polymer gels suchas cellulose esters. The preparation shown includes the use of differentorganic solvents for the cellulose esters. Zeolites are not mentioned aspossible adsorbent powders and the manufacture of the particles requiresan emulsification step in which the adsorbent particle polymer solventmixture is emulsified in an aqueous solution.

I have discovered an improvement to an aqueous separation process inwhich a zeolite containing adsorbent is used which minimizes thedisintegration of the adsorbent and silicon contamination of theproduct.

SUMMARY OF THE INVENTION

Accordingly, the primary objective of my invention is to provide animprovement to a process for the separation of a component from a feedmixture comprising different components in aqueous solution bycontacting said mixture with an adsorbent comprising a zeolite so as tominimize the dissolution of the crystalline aluminosilicate and silicacontamination of the product.

In brief summary, my invention is, in its primary embodiment, a processfor the separation of a component from a feed mixture comprising anaqueous solution of a mixture of components by contacting the solutionwith an adsorbent comprising a zeolite exhibiting an adsorptiveselectivity towards the component, thereby selectively adsorbing thecomponent from the mixture, separating the solution from contact withadsorbent, and thereafter recovering the adsorbed component, bydesorption thereof from the adsorbent, the silicon constituent of thezeolite tending to dissolve in the solution resulting in the undesirabledisintegration of the adsorbent, the improvement which comprises theimpregnation of the zeolite, prior to the contacting with the aqueoussolution, with a water permeable organic polymer binder, therebysubstantially reducing the extent of dissolution of the siliconconstituent and the extent of the disintegration of the zeolite.

Other objects and embodiments of my invention encompass details aboutfeed mixtures, adsorbents, binder materials, solvents, desorbentmaterials and operating conditions, all of which are hereinafterdisclosed in the following discussions of each of the facets of thepresent invention.

DESCRIPTION OF THE INVENTION

At the outset the definitions of various terms used throughout thespecification will be useful in making clear the operation, objects andadvantages of my process.

A feed mixture is a mixture containing one or more extract componentsand one or more raffinate components to be separated by my process. Theterm "feed stream" indicates a stream of a feed mixture which passes tothe adsorbent used in the process.

An "extract component" is a component that is more selectively adsorbedby the adsorbent while a "raffinate component" is a component that isless selectively adsorbed. The term "desorbent material" shall meangenerally a material capable of desorbing an extract component. The term"desorbent stream" or "desorbent input stream" indicates the streamthrough which desorbent material passes to the adsorbent. The term"raffinate stream" or "raffinate output stream" means a stream throughwhich a raffinate component is removed from the adsorbent. Thecomposition of the raffinate stream can vary from essentially 100%desorbent material to essentially 100% raffinate components. The term"extract stream" or "extract output stream" shall mean a stream throughwhich an extract material which has been desorbed by a desorbentmaterial is removed from the adsorbent. The composition of the extractstream, likewise, can vary from essentially 100% desorbent material toessentially 100% extract components. At least a portion of the extractstream, and preferably at least a portion of the raffinate stream, fromthe separation process are passed to separation means, typicallyfractionators or evaporators, where at least a portion of desorbentmaterial is separated to produce an extract product and a raffinateproduct. The terms "extract product" and "raffinate product" meansproducts produced by the process containing, respectively, an extractcomponent and a raffinate component in higher concentrations than thosefound in the extract stream and the raffinate stream.

The term "selective pore volume" of the adsorbent is defined as thevolume of the adsorbent which selectively adsorbs an extract componentfrom the feed mixture. The term "non-selective void volume" of theadsorbent is the volume of the adsorbent which does not selectivelyretain an extract component from the feed mixture. This volume includesthe cavities of the adsorbent which contain no adsorptive sites and theinterstitial void spaces between adsorbent particles. The selective porevolume and the non-selective void volume are generally expressed involumetric quantities and are of importance in determining the properflow rates of fluid required to be passed into an operational zone forefficient operations to take place for a given quantity of adsorbent.When adsorbent "passes" into an operational zone (hereinafter definedand described) employed in one embodiment of this process, itsnon-selective void volume, together with its selective pore volume,carries fluid into that zone. The non-selective void volume is utilizedin determining the amount of fluid which should pass into the same zonein a counter-current direction to the adsorbent to displace the fluidpresent in the non-selective void volume. If the fluid flow rate passinginto a zone is smaller than the non-selective void volume rate ofadsorbent material passing into that zone, there is a net entrainment ofliquid into the zone by the adsorbent. Since this net entrainment is afluid present in non-selective void volume of the adsorbent, it, in mostinstances, comprises less selectively retained feed components. Theselective pore volume of an adsorbent can in certain instances adsorbportions of raffinate material from the fluid surrounding the adsorbent,since in certain instances there is competition between extract materialand raffinate material for adsorptive sites within the selective porevolume. If a large quantity of raffinate material with respect toextract material surrounds the adsorbent, raffinate material can becompetitive enough to be adsorbed by the adsorbent.

The so-called "simple sugars" are classified as monosaccharides and arethose sugars which upon hydrolysis do not break down into smaller simplesugars. One may further classify monosaccharides as aldoses or ketoses,depending upon whether they are hydroxy aldehydes or hydroxy ketones,and by the number of carbon atoms in the molecule. Most common and wellknown are probably the hexoses. Common ketohexoses are fructose(levulose) and sorbose; common aldohexoses are glucose (dextrose),mannose and galactose. The term "oligosaccharides", as commonlyunderstood in the art and as used herein, means simple polysaccharidescontaining a known number of constituent monosaccharide units. Anoligosaccharide that breaks up upon hydrolysis into two monosaccharideunits is called a disaccharide, examples being sucrose, maltose, andlactose. Those giving three such units are trisaccharides, of whichraffinose and melezitose are examples. Di-, ti- and tetra-saccharidescomprise practically all of the oligosaccharides. The term"polysaccharide" includes oligosaccharides but usually it refers tocarbohydrate materials of much higher molecular weight, namely, thosethat are capable of breaking up on hydrolysis into a large number ofmonosaccharide units. Typical polysaccharides are starch, glycogen,cellulose and pentosans.

Feed mixtures which can be charged to the process of my invention may,for example, be aqueous solutions of one or more aldoses and one or moreketoses, or one or more monosaccharides and one or moreoligosaccharides. The concentration of solids in the solutions may rangefrom about 0.5 wt. % to about 50 wt. % or more, but preferably will befrom about 5 wt. % to about 35 wt. %. Starch syrups such as corn syrupare examples of feed mixtures which can be charged to my process. Suchsyrups are produced by the partial hydrolysis of starch generally in thepresence of mineral acids or enzymes. Corn syrup produced in this mannerwill typically contain 25 wt. % to 75 wt. % solids comprising 90% to 95%glucose and 5% to 10% maltose and higher oligosaccharides. A portion ofthe glucose in this corn syrup may be isomerized with an isomerizingenzyme to produce a high-fructose corn syrup, typically comprising40-45% fructose, 50-55% glucose and 5-10% oligosaccharides, which canalso be charged to my process. The pH of the aqueous solution comprisingthe feed mixture may be from about 5.0 to about 8.0.

Desorbent materials used in various prior art adsorptive separationprocesses vary depending upon such factors as the type of operationemployed. In the swing-bed system, in which the selectively adsorbedfeed component is removed from the adsorbent by a purge stream,desorbent selection is not as critical and desorbent material comprisinggaseous hydrocarbons such as methane, ethane, etc., or other types ofgases such as nitrogen or hydrogen, may be used at elevated temperaturesor reduced pressures or both to effectively purge the adsorbed feedcomponent from the adsorbent. However, in adsorptive separationprocesses which are generally operated continuously at substantiallyconstant pressures and temperatures to insure liquid phase, thedesorbent material must be judiciously selected to satisfy manycriteria. First, the desorbent material should displace an extractcomponent from the adsorbent with reasonable mass flow rates withoutitself being so strongly adsorbed as to unduly prevent an extractcomponent from displacing the desorbent material in a followingadsorption cycle. Expressed in terms of the selectivity (hereinafterdiscussed in more detail), it is preferred that the adsorbent be moreselective for all of the extract components with respect to a raffinatecomponent than it is for the desorbent material with respect to araffinate component. Secondly, desorbent materials must be compatiblewith the particular adsorbent and the particular feed mixture. Morespecifically, they must not reduce or destroy the critical selectivityof the adsorbent for an extract component with respect to a raffinatecomponent. Additionally, desorbent materials should not chemically reactwith or cause a chemical reaction of either an extract component or araffinate component. Both the extract stream and the raffinate streamare typically removed from the adsorbent in admixture with desorbentmaterial and any chemical reaction involving a desorbent material and anextract component or a raffinate component would reduce the purity ofthe extract product or the raffinate product or both. Since both theraffinate stream and the extract stream typically contain desorbentmaterials, desorbent materials should additionally be substances whichare easily separable from the feed mixture that is passed into theprocess. Without a method of separating at least a portion of thedesorbent material present in the extract stream and the raffinatestream, the concentration of an extract component in the extract productand the concentration of a raffinate component in the raffinate productwould not be very high, nor would the desorbent material be availablefor reuse in the process. It is contemplated that at least a portion ofthe desorbent material will be separated from the extract and theraffinate streams by distillation or evaporation, but other separationmethods such as reverse osmosis may also be employed alone or incombination with distillation or evaporation. Since the raffinate andextract products are foodstuffs intended for human consumption,desorbent materials should also be materials which are readily availableand therefore reasonable in cost.

I have found that water having a PH of from about 5.0 to about 8.0satisfies these criteria and is a suitable and preferred desorbentmaterial for my process. The pH of the desorbent material is importantbecause adsorption of a component by the adsorbent, removal of araffinate stream, desorption of the component from the adsorbent andremoval of an extract stream all typically occur in the presence ofdesorbent material. If the desorbent material is too acidic or tooalkaline, chemical reactions of the components are promoted and reactionproducts are produced that can reduce the yield purity of either theextract or raffinate product, or both.

Water pH does of course vary widely depending upon the source of thewater in addition to other factors. Methods of maintaining andcontrolling a desired water pH are, however, well known to those skilledin the art of water treating. Such methods generally comprise adding analkaline compound such as sodium hydroxide or an acid compound such ashydrochloric acid to the water in amounts as necessary to achieve andmaintain the desired pH.

The prior art has recognized that certain characteristics of adsorbentsare highly desirable, if not absolutely necessary, to the successfuloperation of a selective adsorption process. Such characteristics areequally important to this process. Among such characteristics are:adsorptive capacity for some volume of an exract component per volume ofadsorbent; the selective adsorption of an extract component with respectto a raffinate component and the desorbent material; and sufficientlyfast rates of adsorption and desorption of an extract component to andfrom the adsorbent. Capacity of the adsorbent for adsorbing a specificvolume of an extract component is, of course, a necessity; without suchcapacity the adsorbent is useless for adsorptive separation.Furthermore, the higher the adsorbent's capacity for an extractcomponent the better is the adsorbent. Increased capacity of aparticular adsorbent makes it possible to reduce the amount of adsorbentneeded to separate an extract component of known concentration containedin a particular charge rate of feed mixture. A reduction in the amountof adsorbent required for a specific adsorptive separation reduces thecost of the separation process. It is important that the good initialcapacity of the adsorbent be maintained during actual use in theseparation process over some economically desirable life. The secondnecessary adsorbent characteristic is the ability of the adsorbent toseparate components of the feed; or, in other words, that the adsorbentpossess adsorptive selectivity, (B), for one component as compared toanother component. Relative selectivity can be expressed not only forone feed component as compared to another but can also be expressedbetween any feed mixture component and the desorbent material. Theselectivity, (B), as used throughout this specification is defined asthe ratio of the two components of the adsorbed phase over the ratio ofthe same two components in the unadsorbed phase at equilibriumconditions. Relative selectivity is shown as Equation 1 below: ##EQU1##where C and D are two components of the feed represented in volumepercent and the subscripts A and U represent the adsorbed and unadsorbedphases respectively. The equilibrium conditions were determined when thefeed passing over a bed of adsorbent did not change composition aftercontacting the bed of adsorbent. In other words, there was no nettransfer of material occurring between the unadsorbed and adsorbedphases. Where selectivity of two components approaches 1.0 there is nopreferential adsorption of one component by the adsorbent with respectto the other; they are both adsorbed (or non-adsorbed) to about the samedegree with respect to each other. As the (B) becomes less than orgreater than 1.0 there is a preferential adsorption by the adsorbent forone component with respect to the other. When comparing the selectivityby the adsorbent of one component C over component D, a (B) larger than1.0 indicates preferential adsorption of component C within theadsorbent. A (B) less than 1.0 would indicate that component D ispreferentially adsorbed leaving an unadsorbed phase richer in componentC and an adsorbed phase richer in component D. Ideally, desorbentmaterials should have a selectivity equal to about 1 or slightly lessthan 1 with respect to all extract components so that all of the extractcomponents can be desorbed as a class with reasonable flow rates ofdesorbent material and so that extract components can displace desorbentmaterial in a subsequent adsorption step. While separation of an extractcomponent from a raffinate component is theoretically possible when theselectivity of the adsorbent for the extract component with respect tothe raffinate component is greater than 1.0, it is preferred that suchselectivity be greater than 1.0. Like relative volatility, the higherthe selectivity the easier the separation is to perform. Higherselectivities permit a smaller amount of adsorbent to be used. The thirdimportant characteristic is the rate of exchange of the extractcomponent of the feed mixture material or, in other words, the relativerate of desorption of the extract component. This characteristic relatesdirectly to the amount of desorbent material that must be employed inthe process to recover the extract component from the adsorbent; fasterrates of exchange reduce the amount of desorbent material needed toremove the extract component and therefore permit a reduction in theoperating cost of the process. With faster rates of exchange, lessdesorbent material has to be pumped through the process and separatedfrom the extract stream for reuse in the process.

Adsorbents to be used in the process of this invention will comprisespecific zeolites. Particular zeolites encompassed by the presentinvention include crystalline aluminosilicate cage structures in whichthe alumina and silica tetrahedra are intimately connected in an openthree dimensional network to form cage-like structures with window-likepores of about 8 Å free diameter. The tetrahedra are cross-linked by thesharing of oxygen atoms with spaces between the tetrahedra occupied bywater molecules prior to partial or total dehydration of this zeolite.The dehydration of the zeolite results in crystals interlaced with cellshaving molecular dimensions and thus the crystalline aluminosilicatesare often referred to as "molecular sieves", particularly when theseparation which they effect is dependent essentially upon differencesbetween the sizes of the feed molecules as, for instance, when smallernormal paraffin molecules are separated from larger isoparaffinmolecules by using a particular molecular sieve.

In hydrated form, the crystalline aluminosilicates used in the processof my invention generally encompass those zeolites represented by theFormula 1 below:

FORMULA 1 M_(2/n) O:Al₂ O₃ :wSiO₂ :yH₂ O

where "M" is a cation which balances the electrovalence of thealuminum-centered tetrahedra and which is generally referred to as anexchangeable cationic site, "n" represents the valence of the cation,"w" represents the moles of SiO₂, and "y" represents the moles of water.The generalized cation "M" may be monovalent, divalent or trivalent ormixtures thereof.

The prior art has generally recognized that adsorbents comprising X andY zeolites can be used in certain adsorptive separation processes. Thesezeolites are described and defined in U.S. Pat. Nos. 2,882,244 and3,130,007 respectively incorporated herein by reference thereto. The Xzeolite in the hydrated or partially hydrated form can be represented interms of mole oxides as shown in Formula 2 below:

FORMULA 2 (0.9±0.2)M_(2/n) O:Al₂ O₃ :(2.50±0.5)SiO₂ :yH₂ O

where "M" represents at least one cation having a valence of not morethan 3, "n" represents the valence of "M", and "y" is a value up toabout 9 depending upon the identity of "M" and the degree of hydrationof the crystal. As noted from Formula 2, the SiO₂ /Al₂ O₃ mole ratio ofX zeolite is 2.5±0.5. The cation "M" may be one or more of a number ofcations such as a hydrogen cation, an alkali metal cation, or analkaline earth cation, or other selected cations, and is generallyreferred to as an exchangeable cationic site. As the X zeolite isinitially prepared, the cation "M" is usually predominately sodium, thatis, the major cation at the exchangeable cationic sites is sodium andthe zeolite is therefore referred to as a sodium-X zeolite. Dependingupon the purity of the reactants used to make the zeolite, other cationsmentioned about may be present, however, as impurities. The Y zeolite inthe hydrated or partially hydrated form can be similarly represented interms of mole oxides as in Formula 3 below:

FORMULA 3 (0.9±0.2) M_(2/n) O:Al₂ O₃ :wSiO₂ :yH₂ O

where "M" is at least one cation having a valence not more than 3, "n"represents the valence of "M", "w" is a value greater than about 3 up toabout 6, and "y" is a value up to about 9 depending upon the identity of"M" and the degree of hydration of the crystal. The SiO₂ /Al₂ O₃ moleratio for Y zeolites can thus be from about 3 to about 6. Like the Xzeolite, the cation "M" may be one or more of a variety of cations but,as the Y zeolite is initially prepared, the cation "M" is also usuallypredominately sodium. A Y zeolite containing predominately sodiumcations at the exchangeable cationic sites is therefore referred to as asodium-Y zeolite.

Cations occupying exchangeable cationic sites in the zeolite may bereplaced with other cations by ion exchange methods well known to thosehaving ordinary skill in the field of crystalline aluminosilicates. Suchmethods are generally performed by contacting the zeolite or anadsorbent material containing the zeolite with an aqueous solution ofthe soluble salt of the cation or cations desired to be placed upon thezeolite. After the desired degree of exchange takes place, the sievesare removed from the aqueous solution, washed, and dried to a desiredwater content. By such methods the sodium cations and any non-sodiumcations which might be occupying exchangeable sites as impurities in asodium-X or sodium-Y zeolite can be partially or essentially completelyreplaced with other cations. It is preferred that the zeolite used inthe process of my invention contain cations at exchangeable cationicsites selected from the group consisting of the alkali metals and thealkaline earth metals.

Typically, adsorbents known to the prior art used in separativeprocesses contain zeolite crystals and amorphous material. The zeolitewill typically be present in the adsorbent in amounts ranging from about75 wt. % to about 98 wt. % based on volatile free composition. Volatilefree compositions are generally determined after the adsorbent has beencalcined at 900° C. in order to drive off all volatile matter. Theremainder of the adsorbent will generally be an amorphous inorganicmaterial such as silica, or silica-alumina mixtures or compounds, suchas clays, which material is present in intimate mixture with the smallparticles of the zeolite material. This amorphous material may be anadjunct of the manufacturing process for zeolite (for example,intentionally incomplete purification of either zeolite during itsmanufacture) or it may be added to relatively pure zeolite, but ineither case its usual purpose is as a binder to aid in forming oragglomerating the hard crystalline particles of the zeolite. Normally,the adsorbent will be in the form of particles such as extrudates,aggregates, tablets, macrospheres or granules having a desired particlesize range. The typical adsorbent will have a particle size range ofabout 16-40 mesh (Standard U.S. Mesh). Examples of zeolites used inadsorbents known to the art, either as is or after cation exchange, are"Molecular Sieves 13X" and "SK-40" both of which are available from theLinde Company, Tonawanda, N.Y. The first material of course contains Xzeolite while the latter material contains Y zeolite. It is known that Xor Y zeolites possess the selectivity requirement and other necessaryrequirements previously discussed and are therefore suitable for use inseparation processes.

The adsorbent of my invention has incorporated therein a binder materialcomprising a water permeable organic polymer. To be water permeable, theorganic polymer, when a dry solid, will have throughout its mass smallvoid spaces and channels which will allow an aqueous solution topenetrate the polymer and thereby come into contact with the zeoliteparticles bound by the polymer. I have found cellulose nitrate and/orcellulose esters such as cellulose acetate to be particularly suitablefor use in the adsorbent of my invention. The preferred concentration ofthe organic polymer in the adsorbent is from about 3.0 wt. % to about50.0 wt. %.

Like some of the above discussed adsorbents of the known art, theadsorbent of my invention is in the form of particles having a particlesize range of about 16-80 mesh (Standard U.S. Mesh). Unlike the knownart adsorbents, however, the adsorbents of my invention do not requirecalcining, and, most important, achieve substantially reduceddisintegration and silicon contamination of the product stream when usedin the process of my invention. The reduced disintegration results inminimization of the undesirable increase in pressure drop through thecolumn in which the adsorbent is packed as compared to the inevitablehigh increase associated with the adsorbents of the known art.

The adsorbent of my invention is manufactured by mixing together powderof the crystalline aluminosilicate, powder of the water soluble organicpolymer binder, and a liquid organic solvent to make the mixturemalleable, forming the mixture into discrete formations, removing thesolvent from the formations and breaking the formations into the desiredsized particles. The forming of the malleable mixture is preferably doneby extrusion. The aluminosilicate and binder powders may first be mixedtogether and the solvent added to the powder mixture, or the binderpowder may be first dissolved in the solvent and the aluminosilicatepowder added to the solution. Preferred liquid organic solvents areacetic acid, methyl amy ketone, 5-methyl-2-hexanone, p-dioxane,methyl-ethyl ketone, acetone, chloroform, benzyl alcohol, ethyl acetateand cyclohexanone, any of which may be mixed with formamide. The solventis removed from the formations either by water washing followed bydrying at a temperature not exceeding about 100° C., or by just dryingat the temperature. The formations are broken into particles having apreferred size such that the particles will pass through a No. 16 screenand be retained on a No. 80 screen. Any fines resulting from thebreaking of the particles not retained on a No. 80 screen may be addedto the aluminosilicate-solvent-binder mixture. The particles may befurther treated to effect ion exchange between cations at exchangeablecationic sites on the crystalline aluminosilicate in the particles andcations preferably selected from the group consisting of alkali metalsand alkaline earth metals.

I have found that merely coating a conventional clay bound adsorbentwith an organic polymer will not result in the improved adsorbent of myinvention. The advantageous effects of the adsorbent of my invention arerealized only when the organic polymer is incorporated into theadsorbent in lieu of the conventional inorganic binder.

With further regard to the aforementioned prior art, U.S. Pat. No.3,262,890 discloses cellulose acetate binder, but that is merely part ofthe discussion in that reference of the prior art relating to molecularsieve adsorbents previously used in the drier cartridges ofrefrigeration systems. The patentees point out that the celluloseacetate and other prior art binders have certain objections which areovercome by the use of a clay mineral as the binder in accordance withtheir invention. Thus, U.S. Pat. No. 3,262,890 does not teach the use ofcellulose acetate or other water permeable organic polymer binder in theseparation process of the present invention for the purpose of reducingdissolution of the silicon component and resultant disintegration of thezeolite adsorbent incident to the contact of the latter with the aqueoussolution being treated in the separation process.

U.S. Pat. No. 3,951,859 teaches the use of cellulose acetate to providewater permeability and mechanical strength to an adsorbent. However, theadsorbents of this reference are not the zeolites employed by thepresent invention and the patentees do not teach the use of thesezeolites in the separation process of the present invention. Therefore,this reference gives no hint to the reduction of silicon dissolutionfrom and disintegration of a zeolite adsorbent resulting from contact ofthe latter with the aqueous solution undergoing treatment in aseparation process. Moreover, it is to be noted that the molecular sieveof this reference contains the adsorbent powder dispersed in a matrix ofpolymer gel prepared in a rather specific manner. That is not theadsorbent material of the present invention which is a zeoliteimpregnated with the water permeable organic polymer binder.

The adsorbent may be employed in the form of a dense compact fixed bedwhich is alternatively contacted with the feed mixture and desorbentmaterials. In the simplest embodiment of the invention, the adsorbent isemployed in the form of a single static bed in which case the process isonly semi-continuous. In another embodiment, a set of two or more staticbeds may be employed in fixed-bed contacting with appropriate valving sothat the feed mixture is passed through one or more adsorbent beds whilethe desorbent materials can be passed through one or more of the otherbeds in the set. The flow of feed mixture and desorbent materials may beeither up or down through the desorbent. Any of the conventionalapparatus employed in static bed fluid-solid contacting may be used.

Counter-current moving-bed or simulated moving-bed counter-current flowsystems, however, have a much greater separation efficiency than fixedadsorbent bed systems and are therefore preferred for use in myseparation process. In the moving-bed or simulated moving-bed processesthe adsorption and desorption operations are continuously taking placewhich allows both continuous production of an extract and a raffinatestream and the continual use of feed and desorbent streams. Onepreferred embodiment of this process utilizes what is known in the artas the simulated moving-bed counter-current flow system. The operatingprinciples and sequence of such a flow system are described in U.S. Pat.No. 2,985,589 incorporated herein by reference thereto. In such asystem, it is the progressive movement of multiple liquid access pointsdown an adsorbent chamber that simulates the upward movement ofadsorbent contained in the chamber. Only four of the access lines areactive at any one time; the feed input stream, desorbent inlet stream,raffinate outlet stream, and extract outlet stream access lines.Coincident with this simulated upward movement of the solid adsorbent isthe movement of the liquid occupying the void volume of the packed bedof adsorbent. So that counter-current contact is maintained, a liquidflow down the adsorbent chamber may be provided by a pump. As an activeliquid access point moves through a cycle, that is, from the top of thechamber to the bottom, the chamber circulation pump moves throughdifferent zones which require different flow rates. A programmed flowcontroller may be provided to set and regulate these flow rates.

The active liquid access points effectively divided the adsorbentchamber into separate zones, each of which has a different function. Inthis embodiment of my process, it is generally necessary that threeseparate operational zones be present in order for the process to takeplace although in some instances an optional fourth zone may be used.

The adsorption zone, zone 1, is defined as the adsorbent located betweenthe feed inlet stream and the raffinate outlet stream. In this zone, thefeedstock contacts the adsorbent, an extract component is adsorbed, anda raffinate stream is withdrawn. Since the general flow through zone 1is from the feed stream which passes into the zone to the raffinatestream which passes out of the zone, the flow in this zone is consideredto be a downstream direction when proceeding from the feed inlet to theraffinate outlet streams.

Immediately upstream with respect to fluid flow in zone 1 is thepurification zone, zone 2. The purification zone is defined as theadsorbent between the extract outlet stream and the feed inlet stream.The basic operations taking place in zone 2 are the displacement fromthe non-selective void volume of the adsorbent of any raffinate materialcarried into zone 2 by the shifting of adsorbent into this zone and thedesorption of any raffinate material adsorbed within the selective porevolume of the adsorbent or adsorbed on the surfaces of the adsorbentparticles. Purification is achieved by passing a portion of extractstream material leaving zone 3 into zone 2 at zone 2's upstreamboundary, the extract outlet stream, to effect the displacement ofraffinate material. The flow of material in zone 2 is in a downstreamdirection from the extract outlet stream to the feed inlet stream.

Immediately upstream of zone 2 with respect to the fluid flowing in zone2 is the desorption zone or zone 3. The desorption zone is defined asthe adsorbent between the desorbent inlet and the extract outlet stream.The function of the desorption zone is to allow a desorbent materialwhich passes into this zone to displace the extract component which wasadsorbed upon the adsorbent during a previous contact with feed in zone1 in a prior cycle of operation. The flow of fluid in zone 3 isessentially in the same direction as that of zones 1 and 2.

In some instances, an optional buffer zone, zone 4, may be utilized.This zone, defined as the adsorbent between the raffinate outlet streamand the desorbent inlet stream, if used, is located immediately upstreamwith respect to the fluid flow to zone 3. Zone 4 would be utilized toconserve the amount of desorbent utilized in the desorption step since aportion of the raffinate stream which is removed from zone 1 can bepassed into zone 4 to displace desorbent material present in that zoneout of that zone into the desorption zone. Zone 4 will contain enoughadsorbent so that raffinate material present in the raffinate streampassing out of zone 1 and into zone 4 can be prevented from passing intozone 3, thereby contaminating extract stream removed from zone 3. In theinstances in which the fourth operational zone is not utilized, theraffinate stream passed from zone 1 to zone 4 must be carefullymonitored in order that the flow directly from zone 1 to zone 3 can bestopped when there is an appreciable quantity of raffinate materialpresent in the raffinate stream passing from zone 1 into zone 3 so thatthe extract outlet stream is not contaminated.

A cyclic advancement of the input and output streams through the fixedbed of adsorbent can be accomplished by utilizing a manifold system inwhich the valves in the manifold are operated in a sequential manner toeffect the shifting of the input and output streams, thereby allowing aflow of fluid with respect to solid adsorbent in a counter-currentmember. Another mode of operation which can effect the counter-currentflow of solid adsorbent with respect to fluid involves the use of arotating disc valve in which the input and output streams are connectedto the valve and the lines through which feed input, extract output,desorbent input and raffinate output streams pass are advanced in thesame direction through the adsorbent bed. Both the manifold arrangementand disc valve are known in the art. Specifically, rotary disc valveswhich can be utilized in this operation can be found in U.S. Pat. Nos.3,040,777 and 3,422,848. Both of the aforementioned patents disclose arotary type connection valve in which the suitable advancement of thevarious input and output streams from fixed sources can be achievedwithout difficulty.

In many instances, one operational zone will contain a much largerquantity of adsorbent than some other operational zone. For instance, insome operations the buffer zone can contain a minor amount of adsorbentas compared to the adsorbent required for the adsorption andpurification zones. It can also be seen that in instances in whichdesorbent is used which can easily desorb extract material from theadsorbent that a relatively small amount of adsorbent will be needed ina desorption zone as compared to the adsorbent needed in the buffer zoneor adsorption zone or purification zone or all of them. Since it is notrequired that the adsorbent be located in a single column, the use ofmultiple chambers or a series of columns is within the scope of theinvention.

It is not necessary that all of the input or output streams besimultaneously used, and in fact, in many instances some of the streamscan be shut off while others effect an input or output of material. Theapparatus which can be utilized to effect the process of this inventioncan also contain a series of individual beds connected by connectingconduits upon which are placed input or output taps to which the variousinput or output streams can be attached and alternately and periodicallyshifted to effect continuous operation. In some instances, theconnecting conduits can be connected to transfer taps which during thenormal operations do not function as a conduit through which materialpasses into or out of the process.

It is contemplated that at least a portion of the extract output streamwill pass into a separation means wherein at least a portion of thedesorbent material can be separated to produce an extract productcontaining a reduced concentration of desorbent material. Preferably,but not necessary to the operation of the process, at least a portion ofthe raffinate output stream will also be passed to a separation meanswherein at least a portion of the desorbent material can be separated toproduce a desorbent stream which can be reused in the process and araffinate product containing a reduced concentration of desorbentmaterial. The separation means will typically be a fractionation columnor an evaporator, the design and operation of either being well known tothe separation art.

Reference can be made to D. B. Broughton U.S. Pat. No. 2,985,589, and toa paper entitled "Continuous Adsorptive Processing--A New SeparationTechnique" by D. B. Broughton presented at the 34th Annual Meeting ofthe Society of Chemical Engineers at Tokyo, Japan, on Apr. 2, 1969, forfurther explanation of the simulated movingbed counter-current processflow scheme.

A dynamic testing apparatus is employed to test various adsorbents witha particular feed mixture and desorbent material to measure theadsorbent characteristics of adsorptive capacity, selectivity andexchange rate. The apparatus consists of an adsorbent chamber ofapproximately 70 cc volume having inlet and outlet portions at oppositeends of the chamber. The chamber is contained within a temperaturecontrol means and, in addition, pressure control equipment is used tooperate the chamber at a constant predetermined pressure. Quantitativeand qualitative analytical equipment such as refractometers,polarimeters and chromatographs can be attached to the outlet line ofthe chamber and used to detect quantitatively or determine qualitativelyone or more components in the effluent stream leaving the adsorbentchamber. A pulse test, performed using this apparatus and the followinggeneral procedure, is used to determine selectivities and other data forvarious adsorbent systems. The adsorbent is filled to equilibrium with aparticular desorbent material by passing the desorbent material throughthe adsorbent chamber. At a convenient time, a pulse of feed containingknown concentrations of a tracer and of a particular ketose or aldose orboth all diluted in desorbent is injected for a duration of severalminutes. Desorbent flow is resumed, and the tracer and the ketose andaldose are eluted as in a liquid-solid chromatographic operation. Theeffluent can be analyzed on-stream or alternatively effluent samples canbe collected periodically and later analyzed separately by analyticalequipment and traces of the envelopes of corresponding component peaksdeveloped.

From information derived from the test adsorbent, performance can berated in terms of void volume, retention volume for an extract or araffinate component, selectivity for one component with respect to theother, the rate of desorption of an extract component by the desorbentand the extent of silica contamination of the extract and raffinatestream. The retention volume of an extract or a raffinate component maybe characterized by the distance between the center of the peak envelopeof an extract or a raffinate component and the peak envelope of thetracer component or some other known reference point. It is expressed interms of the volume in cubic centimeters of desorbent pumped during thistime interval represented by the distance between the peak envelope.Selectivity, (B), for an extract component with respect to a raffinatecomponent may be characterized by the ratio of the distance between thecenter of the extract component peak envelope and the tracer peakenvelope (or other reference point) to the corresponding distancebetween the center of the raffinate component peak envelope and thetracer peak envelope. The rate of exchange of an extract component withthe desorbent can generally be characterized by the width of the peakenvelopes at half intensity. The narrower the peak width the faster thedesorption rate.

To further evaluate promising adsorbent systems and to translate thistype of data into a practical separation process requires actual testingof the best system in a continuous counter-current moving-bed orsimulated moving-bed liquid-solid contacting device. The generaloperating principles of such a device are as described hereinabove. Aspecific laboratory-size apparatus utilizing these principles isdescribed in deRosset et al U.S. Pat. No. 3,706,812. The equipmentcomprises multiple adsorbent beds with a number of access lines attachedto distributors within the beds and terminating at a rotary distributingvalve. At a given valve position, feed and desorbent are beingintroduced through two of the lines and the raffinate and extractstreams are being withdrawn through two more. All remaining access linesare inactive when the position of the distributing valve is advanced byone index all active positions will be advanced by one bed. Thissimulates a condition in which the adsorbent physically moves in adirection countercurrent to the liquid flow. Additional details on theabove-mentioned adsorbent testing apparatus and adsorbent evaluationtechniques may be found in the paper "Separation of C₈ Aromatics byAdsorption" by A. J. deRosset, R. W. Neuzil, D. J. Korous, and D. H.Rosback presented at the American Chemical Society, Los Angeles,California, March 28 through Apr. 2, 1971.

Although both liquid and vapor phase operations can be used in manyadsorptive separation processes, liquid-phase operation is required forthis process because of the lower temperature requirements and becauseof the higher yields of extract product that can be obtained withliquid-phase operation over those obtained with vapor-phase operation.Adsorption conditions will include a temperature range of from about 20°C. to about 200° C. with about 20° C. to about 100° C. being morepreferred and a pressure range of from about atmospheric to about 500psig with from about atmospheric to about 250 psig being more preferredto insure liquid phase. Desorption conditions will include the samerange of temperatures and pressures as used for adsorption conditions.

The size of the units which can utilize the process of this inventioncan vary anywhere from those of pilot-plant scale (see for example ourassignee's U.S. Pat. No. 3,706,812) to those of commercial scale and canrange in flow rates from as little as a few cc an hour up to manythousands of gallons per hour.

The following examples are presented to illustrate my invention and arenot intended to unduly restrict the scope and spirit of the claimsattached hereto.

EXAMPLE I

The purpose of this example is to illustrate the method of manufactureof adsorbents of my invention. Five different adsorbent samples wereprepared, each such preparation by the following steps:

(1) Na-Y zeolite powder was mixed with an organic polymer comprisingcellulose acetate powder for four of the samples, or with celluloseacetate and cellulose nitrate for one of the samples.

(2) An organic solvent was added to the powder mixture slowly and withmulling to obtain an extrudable mixture.

(3) The extrudable mixture was extruded into an extrudate.

(4) The extrudate was dried at 65° C.

(5) The dried extrudate was granulated and screened so as to obtainparticles sized from 30 to 60 mesh.

(6) The cations occupying exchangeable cationic sites in the zeolitecontained in the particles were ion exchanged with calcium ions bycontacting the particles with an aqueous solution of calcium chloride,washing the particles with fresh deionized water and air, and drying theparticles at room temperature.

The following Table 1 sets forth details concerning the materials andamounts thereof used in the preparation of the above five adsorbents.

                  TABLE 1                                                         ______________________________________                                             Na--Y    Organic Polymer (gm)     Forma-                                      Zeolite  (Cellulose Acetate       mide                                   No.  (gm)     except as noted)                                                                              Solvent (ml)                                                                           (ml)                                   ______________________________________                                        1    207.65   75              450 (acetone)                                                                          80                                     2    124.6    45              280 (acetone)                                                                           0                                     3    124.6    25 gm cellulose acetate                                                                       280 (acetone)                                                                          20                                                   25 gm cellulose nitrate                                         4    124.6    81              300 (acetone)                                                                          20                                     5    124.6      26.47         200 (acetone)                                                                          20                                     ______________________________________                                    

EXAMPLE II

The purpose of this example is to present the results of tests of eachof the adsorbents, prepared as set forth in the above Example I, in thedynamic testing apparatus hereinbefore described to determine theperformance of each such adsorbent with regard to the adsorptiveseparation of the individual components of an aqueous solution of amixture of components. Also tested for purposes of comparison with theabove five adsorbents of my invention were a conventional 20% clay boundcalcium exchanged zeolite adsorbent and the same conventional adsorbentcoated with cellulose acetate.

The general pulse-test apparatus and procedure have been previouslydescribed. In this case, however, no on-stream GC analyzer was used tomonitor the effluent. Instead, the effluent was collected in anautomatic sample collector, and later each sample was injected into ahigh pressure liquid chromatograph (HPLC) for analysis. Each sample wascollected for a two minute period, and unlike the almost instantaneouscomponent concentration obtained with an on-stream GLC, each samplerepresented an average of the component concentration over the twominute period of time.

The adsorbent test column consisted of a stainless steel tube 127 cmlong and 8.4 mm in internal diameter. This resulted in a test adsorbentbed of 70 cc. The feed consisted of 5 wt. % each of glucose, fructoseand sucrose and 20 vol. % of D₂ O (deuterium oxide) in deionized water.The desorbent was deionized water with a nominal pH value of 7.0.

The desorbent was run continuously at a rate of 1 ml/min. Both feed anddesorbent were pumped under capillary flow control. At some convenienttime interval, the desorbent was stopped and the feed which was also runat a rate of 1 ml/min. was pumped for a period of 10 min. to deliver a10 ml "pulse". Immediately after the feed pulse was completed, thedesorbent flow was resumed and sample collection was begun. The twominute samples were collected for a period of 90 minutes, for a total of45 samples.

The effluent fractions were then sequentially injected into the HPLC foranalysis. From the analysis of these fractions, a chromatograph of theseparation of the feed components that were present in the feed pulsewere constructed. This was accomplished by plotting the peak height ofeach component versus the volume of effluent represented by the fractionfrom which the measurements were made. By joining the respective peakheights of each component, peak envelopes of the components wereobtained. The composite plot resembled a chromatogram of component peaksobtained from an analytical GC or LC of poor resolving power.

The sucrose, which is a disaccharide, evidently cannot enter the smallerselective pores of the adsorbent that the monosaccharides glucose andfructose can enter. Thus, the retention volume of the sucrose asmeasured, from the center of its peak envelope to the point where thefeed pulse was injected, was a measure of the void volume of the bed.The center of the sucrose peak envelope also served as the zero pointfor measuring the net retention volumes of the glucose, fructose and D₂O. The ratio of these net retention volumes was a measure of theselectivity, (B), of the adsorbent for the more strongly adsorbedcomponent (larger net retention volume) with respect to the componentthat was less strongly adsorbed (smaller net retention volume).

The use of D₂ O (deuterium oxide) in this test allowed the measurementof the selectivity between the desorbent, water, and the more stronglyadsorbed component or extract, which was fructose. The ideal desorbentfor the Sorbex process is one that is adsorbed by the adsorbent justslightly less than the extract component, and more strongly than themost strongly adsorbed component that is rejected into the raffinate. Ingeneral, a selectivity of 1.1 to 1.4 for the extract component withrespect to the desorbent is ideal. The results for these pulse tests areshown in Table 2 below. The reference numbers of the five adsorbents arethe same as the reference numbers of the corresponding adsorbents ofExample I.

                                      TABLE 2                                     __________________________________________________________________________                 Conventional                                                                          Adsorbent                                                                            Adsorbent                                                                            Adsorbent                                                                            Adsorbent No.                                                                          Adsorbent                  Conventional Coated W/1%                                                                           No. 5 (17.5%                                                                         No. 1 (26.5%                                                                         No. 2 (26.5%                                                                         (14.3% Cellulose                                                                       No. 4 (39.4%               (20% Clay    Cellulose                                                                             Cellulose                                                                            Cellulose                                                                            Cellulose                                                                            Acetate, 14.3%                                                                         Cellulose                  Binder)      Acetate Acetate)                                                                             Acetate)                                                                             Acetate)                                                                             Cellulose Nitrate)                                                                     Acetate)                   __________________________________________________________________________    HALF WIDTH (ml)                                                               Fructose                                                                            14     16.4    13.4   11.8   14     13.4     13.2                       Glucose                                                                             12     13.6    12.0   12.8   16.2   15.6     11.6                       Sucrose                                                                             12.6   14.6    12.8   14     15.6   16       12.4                       D.sub.2 O                                                                           10     5.4     8.9    6      10.8   10.4     9.2                        RETENTION VOLUME (ml)                                                         Fructose                                                                            13.2   13.2    10.30  10     11     9.6      7.2                        Glucose                                                                             2.4    2.4     2.07   1.8    2.4    2        1                          Sucrose                                                                             0      0       0      0      0      0        0                          D.sub.2 O                                                                           12.8   7.8     11.7   11.6   13.4   9.2      9.8                        Fructose/                                                                           5.5    5.5     4.96   5.5    4.6    4.8      7.2                        Glucose                                                                       Fructose/                                                                           1.03   1.14    0.88   0.86   0.82   1.04     0.73                       D.sub.2 O                                                                     __________________________________________________________________________

It is apparent from the data of Table 2 that the performance of theadsorbents of my invention, with regard to adsorption of components froman aqueous system, does not substantially differ from the conventionalclay bound adsorbent or conventional adsorbent coated with celluloseacetate.

EXAMPLE III

The purpose of this example is to present the results of tests forsilica loss of adsorbents of my invention and conventional clay boundadsorbents when contacted with an aqueous stream. The testing apparatuscomprised means for pumping, metering and maintaining a specifictemperature of an aqueous stream; a first and second column each of 20cc capacity in which the adsorbent to be tested was packed; and a firstand second filter. The flow of the aqueous stream was from the pumping,metering and temperature control means through the first column, thenthrough the first filter, then through the second column and finallythrough the second filter. Sample taps enabled sampling of the aqueousstream at points immediately downstream of each filter, the samples fromthe first tap being referred to as "Effluent from Col. No. 7," and thesamples from the second tap being referred to as "Effluent from Col. No.2". The purpose of having two packed columns was to enable adetermination of whether an equilibrium concentration of silicon in theaqueous stream was reached in flowing through the first column, orwhether such equilibrium was not reached and the concentration ofsilicon would continue to increase during flow through the secondcolumn.

Two test runs using the above apparatus were made. For the first run,the columns were packed with the conventional clay bound adsorbentdescribed in Example II, while in the second run the column was packedwith an adsorbent of my invention comprising a faujasite with acellulose acetate binder. Each test run was over an extended period oftime during which samples of the aqueous streams were periodically takenfrom both of the sample taps and analyzed for silicon concentration. Thecumulative amount of effluent from the apparatus was measured at eachtime samples were taken and noted as "Total Raff". The filters werechanged whenever they became plugged with particulate matter. Thefollowing Tables 3 and 4 present the data obtained from the first runand second run, respectively.

                                      TABLE 3                                     __________________________________________________________________________         Effluent                                                                           Effluent                                                                 from from Total                                                                              LHSV Based                                                Hours on                                                                           Col. #1                                                                            Col. #2                                                                            Raff.                                                                              on 20 cc                                                  Stream                                                                             (ppm Si)                                                                           (ppm Si)                                                                           (Liters)                                                                           Col.   Remarks                                            __________________________________________________________________________     18  --   12.7 7.1  20     Adsorbent temperature                                                         68° C. throughout run.                       42  --   12.7 16.6 20                                                         66   8.2 11.3 26.1 20                                                         90   7.5 11.3 35.6 20                                                        114   6.6 10.8 45.1 20                                                        138  --   11.3 54.6 20                                                        162   6.1 10.3 64.1 20     Changed filters 1 & 2.                             186  14.6 18.6 66.7 2.5    Reduced LHSV to 2.5.                               210  15.0 18.3 67.9 2.5                                                       234  13.2 16.9 69.1 2.5                                                       258  12.7 16.0 70.3 2.5                                                       282  11.8 15.5 71.6 2.5                                                       306  12.0 14.8 72.6 2.5                                                       330  12.0 14.8 73.7 2.5                                                       354  --   16.0 74.8 2.5                                                       378  --   16.0 75.9 2.5                                                       402  12.7 15.7 77.0 2.5                                                       426  12.5 15.0 78.3 2.5    Changed filter 1.                                                             Reduced LHSV to 1.25.                              450  13.6 15.5 79.0 1.25                                                      474  13.6 16.5 79.7 1.25                                                      498  13.6 16.4 80.3 1.25                                                      570  13.4 16.5 82.1 1.25                                                      594  13.6 16.5 82.7 1.25                                                                                 Adsorbent weight loss                                                         from Col. #1 is 2.4 g.                                                        and from Col. #2 is                                                           1.0 g.                                             __________________________________________________________________________

                                      TABLE 4                                     __________________________________________________________________________         Effluent                                                                           Effluent                                                                 from from Total                                                                              LHSV Based                                                Hour on                                                                            Col. #1                                                                            Col. #2                                                                            Raff.                                                                              on 20 cc                                                  Stream                                                                             (ppm Si)                                                                           (ppm Si)                                                                           (Liters)                                                                           Col.   Remarks                                            __________________________________________________________________________     18  3.8  7.1  7.1  20     Adsorbent temperature                                                         68° C. throughout run.                       42  3.3  6.1  16.6 20                                                         66  4.2  6.1  26.1 20                                                         90  5.2  5.4  35.6 20     Changed filter 2.                                  114  3.3  3.8  45.1 20                                                        138  3.5  4.7  54.6 20                                                        162  5.6  4.9  64.1 20                                                        186  7.5  9.8  66.7 2.5                                                       210  12.7 10.1 67.9 2.5                                                       234  11.8 10.3 69.1 2.5                                                       258  8.5  8.9  70.3 2.5                                                       282  5.9  8.9  71.6 2.5                                                       306  6.1  9.4  72.6 2.5                                                       330  6.6  9.4  73.7 2.5                                                       354  5.6  9.4  74.8 2.5                                                       378  5.6  10.3 75.9 2.5                                                       402  --   9.9  77.0 2.5                                                       426  5.6  8.5  78.3 2.5                                                       450  7.3  9.9  79.0 1.25                                                      474  7.5  9.9  79.7 1.25                                                      498  7.5  9.4  80.3 1.25                                                      570  7.1  9.2  82.5 1.25                                                      594  7.1  8.9  83.1 1.25                                                                                 Adsorbent weight loss                                                         from Col. #1 is 0.61 g.                                                       and from Col. #2 is                                                           0.36 g.                                            __________________________________________________________________________

From a comparison of the data in the foregoing Tables 3 and 4, it isapparent that less silicon is removed from the adsorbent of my inventionby an aqueous stream than from a conventional adsorbent. Of the twoadsorbents, mine imparts a far smaller concentration of silicon to theaqueous stream and suffers a far smaller dissolution measured by weightloss. Furthermore, in view of a comparison of the frequency at which thefilters had to be changed in the first and second runs, it is clear thatless particulate matter is lost by the adsorbent of my invention in anaqueous stream.

EXAMPLE IV

The purpose of this example is to present data comprising a comparisonbetween the adsorbents prepared in accordance with Example I, aconventional adsorbent having a clay binder, and the same conventionaladsorbent coated with cellulose acetate, when tested in an apparatussimilar to that described in Example II to determine the amount ofsilicon imparted by each such adsorbent to an aqueous stream. Only onecolumn packed with adsorbent was used. The aqueous stream was passedthrough the adsorption column of the apparatus at a temperature of 60°C. and a liquid hourly space velocity (LHSV) of 1.0. The siliconconcentration of the aqueous stream downstream of the column wasmeasured twice for each adsorbent tested, once after 10 hours from thebeginning of the applicable test and once after 74 hours.

                                      TABLE 5                                     __________________________________________________________________________               Conventional,                                                                 Coated W/1%                                                        Conventional                                                                             Cellulose Ace-                                                                        No. 5                                                                             No. 1                                                                             No. 2                                                                             No. 3                                                                             No. 4                                      (ppm Si)   tate (ppm Si)                                                                         (ppm Si)                                                   __________________________________________________________________________    After                                                                             30     30      12  14  16  13  15                                         10 hr.                                                                        After                                                                             15-20  18      --   8  10   9   9                                         74 hr.                                                                        __________________________________________________________________________

It is clear from the data of Table 5 not only that the adsorbent of myinvention imparts far less silica to the aqueous stream than theconventional clay bound adsorbent, but also that merely coating theconventional adsorbent with the organic polymer, rather than using theorganic polymer as the binder material in lieu of clay as taught by myinvention, does not provide any lessening of silica loss.

I claim as my invention:
 1. A process for the separation of a componentfrom a feed mixture comprising an aqueous solution of a mixture ofcomponents, which process comprises(1) contacting said solution toselectively adsorb said component from said mixture, with an adsorbentcomprising a zeolite having impregnated therein a water permeableorganic polymer, the adsorbent exhibiting an adsorptive selectivitytowards said component, where the adsorbent is prepared by the stepsof:(a) mixing together a powder of said zeolite, a powder of said waterpermeable organic polymer and a liquid organic solvent to form amalleable mixture; (b) forming said malleable mixture into discreteformations; (c) removing said solvent from said formation to obtain harddry formations; and, (d) breaking said hard dry formations intoparticles of desired size to obtain said zeolite impregnated with awater permeable organic polymer binder; (2) separating said solutionfrom contact with said adsorbent and (3) recovering said adsorbedcomponent by desorption of the adsorbed component from the adsorbent. 2.The process of claim 1 further characterized in that said waterpermeable organic polymer comprises a cellulose ester or cellulosenitrate.
 3. The process of claim 1 further characterized in that saidzeolite is selected from the group consisting of X zeolites and Yzeolites.
 4. The process of claim 3 further characterized in that saidzeolite contains cations at exchangeable cationic sites selected fromthe group consisting of alkali metals and alkaline earth metals.
 5. Theprocess of claim 1 further characterized in that said feed mixturecomprises an aqueous solution of saccharides.
 6. The process of claim 5further characterized in that said saccharides comprise a mixture offructose and glucose.
 7. The process of claim 5 further characterized inthat recovery of said adsorbed component is effected with a desorbentcomprising water.
 8. The process of claim 5 further characterized inthat the pH of said aqueous solution is from about 5.0 to about 8.0. 9.The process of claim 8 further characterized in that the content of saidorganic polymer in said adsorbent is from about 3.0 wt.% to about 50.0wt.%.
 10. The process of claim 1 wherein said zeolite exhibitingselectivity towards said component has a reduced tendency to dissolve insaid aqueous solution.
 11. The process of claim 1 wherein in step (a)powders of said zeolite and said binder are first mixed together toobtain a powder mixture, and said liquid organic solvents is then addedto said powder mixture to obtain said malleable mixture.
 12. The processof claim 1 wherein the step (a) said powder of said binder is firstdissolved in said organic solvent to obtain a solution, and said powderof said zeolite is then added to said solution to obtain said malleablemixture.
 13. The process of claim 1 wherein in step (c) said solvent isremoved from said formations by first washing said formations with waterand then drying said formations at a temperature not exceeding about100° C.
 14. The process of claim 1 wherein in step (c) said solvent isremoved from said formations by drying said formations at a temperaturenot exceeding about 100° C.
 15. The process of claim 1 wherein in step(d) said desired sizes of said particles is such that said particleswill pass through a No. 16 screen and be retained on a No. 80 screen.16. The process of claim 1 wherein said liquid organic solvent comprisesp-dioxane, methyl-ethyl ketone, ethyl acetone, acetone, chloroform,benzyl alcohol, cyclohexanone, or formamide.
 17. The process of claim 1wherein in step (b) said forming is effected by extrusion.